The present invention relates to location registration methods for mobile radio communication systems, and more particularly, to a location registration method directed to a situation in which a fault occurs in a memory device (home location register: HLR) which stores and manages information concerning the locations of mobile stations and thus the location information is lost.
In a mobile radio communication system, base stations broadcast common information such as a location registration area number to all mobile stations located within cells thereof. The mobile stations refer to the broadcasted information, and watch whether they move to location registration areas different from those in which the mobile stations are located at present. Then, the mobile stations send location registration signals to a mobileservices switching center via the base stations, if the mobile stations move to the different location registration areas. On the basis of the received location registration signals, the mobile services switching center registers, in a home location register HLR, subscriber data on the mobile stations and location information indicating location registration areas in which the mobile stations are located. When a gateway mobileservices switching center receives a call directed to a mobile station, it looks up the location information stored in the home location register HLR, and identifies a mobileservices switching center corresponding to the location registration area in which the called mobile station is located. Then, the gateway mobileservices switching center causes the identified mobileservices switching center to perform simultaneous paging through a plurality of base stations located within the location registration area in which the called mobile station is located.
FIG. 11 schematically shows a mobile radio communication system. Mobile stations MS.sub.1 -MS.sub.6 are terminals which can perform two-way radio communications with base stations BS.sub.1 -BS.sub.6, respectively. The base stations BS.sub.1 -BS.sub.6 can communicate with the mobile stations MS.sub.1 -MS.sub.6 located within radio zones or cells C.sub.1 -C.sub.6 formed around the base stations BS.sub.1 -BS.sub.6, respectively. The radio zones C.sub.1 -C.sub.3 of the base stations BS.sub.1 -BS.sub.3 form a location registration area (or a simultaneous paging area) PRA.sub.1, and the radio zones C.sub.4 -C.sub.6 of the base stations BS.sub.4 -BS.sub.6 form another location registration area (a simultaneous paging area) PRA.sub.2.
Mobileservices switching centers MSC.sub.1 -MSC.sub.2 have the functions of realizing call connecting control and service control directed to providing mobileservices. The mobileservices switching center MSC.sub.1 is connected to the base stations BS.sub.1 -BS.sub.3 and the mobileservices switching center MSC.sub.2 is connected to the base stations BS.sub.4 -BS.sub.6. A gateway mobileservices switching center GS accepts, from another network, calls directed to its own network subscribers or calls directed to roaming subscribers, and is connected to the mobileservices switching centers MSC.sub.1 -MSC.sub.2 located within its own network through communication lines. Further, the gateway mobileservices switching center GS is connected to a home location register HLR via a control signal line in order to make inquiries of the location information.
The home location register HLR is a database which stores subscriber data and location information on the mobile stations MS.sub.1 -MS.sub.6 located in the location registration areas PRA.sub.1 -PRA.sub.2. The mobileservices switching centers MSC.sub.1 -MSC.sub.2 receive the location registration signals from the mobile stations MS.sub.1 -MS.sub.6, so that the contents of the home location register HLR can be updated and new subscriber data and/or location information can be registered therein.
If a call directed to the mobile station MS.sub.1 is received, the home location register HLR is referred to, and the simultaneous paging is carried out by all the base stations BS.sub.1 -BS.sub.3 forming the location registration area PRA.sub.1 in which the called mobile station is located. A backup memory HLR' backs up the contents of the home location register HLR.
FIG. 12 schematically shows a location registering and call receiving sequence in the mobile radio communications.
The base stations BS.sub.1 -BS.sub.3 notify, by using the broadcast information, the mobile stations MS.sub.1 -MS.sub.3 of information concerning location registration. When the mobile station MS.sub.3 (see FIG. 11) which is located in the location registration area PRA.sub.1 moves to the location registration area PRA.sub.2, as shown in FIG. 13, the mobile station MS.sub.3 detects a change of the location registration area by referring to the information broadcasted from the base stations BS.sub.4 -BS.sub.6. Thus, the mobile station MS.sub.3 transmits the location registration signal, which is sent to the mobileservices switching center MSC.sub.2 via any of the base stations BS.sub.4 -BS.sub.6. The mobileservices switching center MSC.sub.2 executes a certifying process upon receiving the location registration signal. If the result of the certifying process is affirmative, the mobileservices switching center MSC.sub.2 instructs the home location register HLR to register a routing number directed to the switching center MSC.sub.2 and the location information indicating the location registration area in which the mobile station MS.sub.3 is located, and sends a location registration admission signal back to the mobile station MS.sub.3. Then, the above location registration sequence executed when the mobile station moves to another location registration area is ended.
When the gateway mobileservices switching center GS receives a call directed to the mobile station MS.sub.3, the switching center GS extracts the subscriber identification number (mobile station identification number) of the mobile station MS.sub.3 from the received dial number. Then, the mobileservices switching center GS reads the location information (routing number) concerning the mobile station MS.sub.3 from the home location register HLR on the basis of the extracted subscriber number, and sets a line to the mobileservices switching center MSC.sub.2 indicated by the routing number. Hence, the mobileservices switching center MSC.sub.2 instructs all the base stations BS.sub.4 -BS.sub.6 in the location registration area PRA.sub.2 to perform the simultaneous paging. In response to the simultaneous paging, the mobile station MS.sub.3 sends an acknowledgement signal to the mobileservices switching center MSC.sub.2 via one of the base stations BS.sub.4 -BS.sub.6. In response to the acknowledgement signal, the mobile services switching center MSC.sub.2 sets up an idle communication channel TCH by a well-known process. Hence, the channel connection is established.
Hence, even if the mobile station moves to anywhere, the location information concerning the location registration area in which the mobile station is located can be updated and validated in the home location register HLR. Thus, calls directed to mobile stations from another network can be accepted.
When the home location register HLR is restarted due to a certain factor such as a fault which occurs therein, all the contents thereof are reset. Hence, a maintenance station copies the contents of the home location register HLR to the backup memory HLR' at predetermined time intervals. The location information can be restored in the home location register HLR by using the backup information. However, the restored location information is only location information available at the restored time, and does not correctly indicate the real locations of the mobiles at the present time. Hence, the location information correctly indicative of the real locations of the mobile stations cannot be restored in the home location register HLR after it is restarted. In this case, calling of the mobile stations may fail. There are three conventional methods in order to modify the restored location information in the home location register HLR and correctly reflect the current situation. The first method is to wait for sending of the location registration signals from the mobile stations. The second method is to wait for the location registration signals sent when the mobile stations moves to different location registration areas. The third method is to prepare a particular message for requesting location registration in the air protocol.
However, the first and second methods have a disadvantage in that the location information cannot be rapidly restored in the home location register HLR. The third method has a disadvantage in that there is a need to provide a particular message in the air protocol and the related control is complicated.